336781 Heads With Flat Top Pistons - Page 2 - Hot Rod Forum : Hotrodders Bulletin Board
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  #16 (permalink)  
Old 07-02-2013, 07:44 PM
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781's with flat tops

If you build a high performance 454 with flat tops, you're gonna have a turd. You need at least 10:1 for any decent performance with those heads especially if you don't open them up with bigger valves and porting. If you have to run low octane go 9.25:1. You have to use domes with those heads. Make sure you get the right pistons for the open chamber heads, don't get pistons for a earlier closed chamber head. If you go large on the cam and spread the lobe separation angle out, you might go 10.5:1 without detonation provided you keep the timing conservative. The heads are not the best but will make some serious HP with good compression ratios. I've built two, one for a car with a roller w/10.5:1 on 93 octane and a one for a boat ~9.25:1 with a milder flat tappet cam and it doesn't rattle on 87 octane.

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Old 07-12-2013, 09:33 PM
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I'm not real crazy, obviously, about discarding my brand new forged flat-tops.

I've just located a set of closed-chamber #3931063 heads, which according to that Mortec achive, are 101cc

Using Summit's compression calculator with these numbers:
4.280 (Bore)
4.00 (Stroke)
101 (Cyl Head Volume)
4.9 (Dome Volume)
0.020 (Deck Clearance)
0.039 (Compressed Gasket Thickness)
8 (# of Cylinders)

... I'm seeing a result of 8.87:1

Can I expect any improvement with my present cam, or should I back it back down at least one level, maybe 2?

The same guy that has the heads has a 454 block bored .060, a set of pistons, rods, and steel crank.


Also has a spread-bore Holley and Weiand Intake


That stuff looks a little sketchy to me, but the ask is $1100.00 for the whole lot. I'm thinking there is almost enough there to build and sell another mill ... or is this just throwing more good money after bad?

I guess it's always hard to give up "known good" parts (even if they might not be a good match) for a bunch of unassembled "unknowns".

Worth the risk? I'm going to go and have a look ... probably on Sunday.
Depending on what he will want for he heads seperately ... I may start with that.

PS.
If I do go with his block, piston, crank, heads ...
4.310 (Bore)
4.00 (Stroke)
101 (Cyl Head Volume)
-0.100 (Dome Volume)
0.025 (?) (Deck Clearance)
0.039 (Compressed Gasket Thickness)
8 (# of Cylinders)

...I'm still only seeing a result of 9.24:1
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Old 07-13-2013, 05:28 AM
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Known good parts??? Consider the possibility he is selling this combo for the same issues hoping to find someone who doesn't know better. Cut to the chase,your bottom line is you do get what you pay for.
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Old 07-14-2013, 12:59 PM
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I bought the heads for $300 / pr. It looks like there are fairly new stainless valves installed along with dual springs. I had looked up some reman ATK heads, and they charge $150.00 core deposit... So worst case scenario is that I have just bought some cores to trade in.
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Old 07-15-2013, 04:29 AM
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Quote:
Originally Posted by BOBCRMAN@aol.com View Post
I read all three of the above sources. LOTS of incorrect information on them..

Example. 049 heads are also listed as 113cc. They are in actuality 120-122..
Another example. Stated in article that tall deck 427 trucks had 7/16" rod bolts. Completely false!

Plus many more. In this case don't believe what is printed..

Yes, I have actually cc'd many BBC heads and they are usually larger than GM stated spec.. I usually start with a .005" cut before measuring the chambers. A sloppy repair valve job can add cc's of volume to the chamber. Sink that valve/seat and add combustion chamber volume..
Sometimes the low-ball volumes are NHRA minimums- NOT what you see on an undecked head.

In any event, the published figures are ball park. ALL heads (both sides) have to be CC'd in order to know exactly what you have.
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